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Microbiology/Immunology > Mechanism of Action of Antibiotics > Flashcards

Mechanism of Action of Antibiotics Flashcards

1
Q

Biochemical Basis of Antimicrobial Action

A
  • bacterial cells grow and divide, replicating repeatedly to reach the large numbers present during an infection or on the surfaces of the body
  • to grow and divide, organisms must synthesize or take up many types of biomolecules
  • antimicrobial agents interfere with specific processes that are essential for growth and/or division
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2
Q

Bactericidal

A

-chemotherapeutic agents that are capable of causing irreversible damage or death to the organism. These agents are independent of the host’s immune system in their action on the organism

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3
Q

Bacteriostatic

A

-agents that inhibit that growth and/or reproduction of the infecting agent, but fail to actually kill the agent. These agents are dependent on the host’s immune system for the elimination of the microorganism

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4
Q

Bactericidal vs Bacteriostatic

A

-bactericidal agents are more effective, but bacteruistatic agents can be extremely beneficial since they permit the normal defenses of the host to destroy the microorganisms

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5
Q

MIC vs MBC

A
  • MIC- minimal inhibitory concentration- represents the lowest concentration of the antibiotic which prevents the organisms from multiplying- not necessarily killing the organism
  • MBC- minimal bacteriocidal concentratin- represents the lowest concentration which kills the organism- not relevant with bacteriostatic agents
  • there is a much closer relationship between the MIC and MBC values for bactericidal drugs than for bacteriostatic drugs
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6
Q

Structures of antibiotics

A
  • B-Lactams- Beta-lectam ring (e.g. penicillins, cephalosporins)
  • aminoglycosides- vary only by side chains attached to basic structure (e.g. gentamycin, tobramycin)
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7
Q

Function of antibiotics

A
  • how the drug works, its mode of action
  • inhibition of cell wall synthesis (most common mechanism- largest class of antibiotics)
  • inhibition of protein synthesis (second largest class)
  • alteration of cell membranes
  • inhibition of nucleic acid synthesis
  • antimetabolite activity
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8
Q

Ideal antibiotic

A
  • selective target- target unique
  • bactericidal- kills
  • narrow spectrum- does not kill normal flora
  • high therapeutic index- ratio of toxic level to therapeutic level
  • few adverse reactions- toxicity, allergy
  • various routes of administration- IV, IM, oral
  • good absorption
  • good distribution to site of infection
  • emergency of resistance is slow
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9
Q

Where will the new antibiotics come from?

A
  • there is a relentless increase in bacterial resistance to currently available antibiotics
  • fever new antibiotics are being developed than ever before
  • only 8 new antibacterial medications have been developed since 1998
  • old: natural products: penicillins, cephalosporins, aminoglycosides, tetracyclines, erythromycin, and related macrolides and vacnomycin and teicoplanin
  • newer: synthetic antibacterials: the second line of antibiotic discovery has come from synthetic chemistry- this is, producing antibacterial agents from structures that are not found in nature
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10
Q

Various antimicrobial agents interfere with

A
  • cell wall synthesis
  • ribosomal function (protein synthesis)
  • plasma membrane integrity
  • nucleic acid synthesis
  • folate synthesis or other metabolic function
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11
Q

Newer Classes of Antibiotics

A
  • Lipoglycopeptides- RX gram positive complicated skin and soft tissue infections
  • Cyclic Lipopeptides- RX gram positive infections- including MRSA
  • Glycylcyclines- RX gram positive (MRSA), gram negatives
  • Oxazolidinones- Rx MRSA and VRE
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12
Q

Gram Positive and Gram Negative Cell Wall composition

A
  • the gram-positive cell wall is composed of a thick, multilayered petidoglycan sheath outside of the cytoplasmic membrane
  • the gram-negative cell wall is composed of an outer membrane linked by lipoproteins to thin, layer of petidoglycan
  • the petidoglycan is located within the periplasmic space that is created between the outer and inner membranes
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13
Q

The bacterial cell wall

A

-Peptidoglycan- a network of N-acetyl Glucosamine and N acetylmuramic acid connected by peptide bonds

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14
Q

Inhibitors of Cell Wall Synthesis

A
  • Beta lactams- penicillins, cephalosporins, monobactams, cerbapenems
  • glycopeptides- vanomycin- gram positive only
  • fosfomycin- UTI’s only
  • Daptomycin- gram positive only, may be used against MRS, VISA, VRSA, VRE
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15
Q

Beta- lactam antibiotics

A
  • beta-lactam antibiotics are among the most commonly prescribed drugs, grouped together based upon a shared structural feature, the beta- lactam ring
  • there are about 50 different B- lactams currently on the market
  • they are all bactericidal
  • they are non-toxic (can be administered at high doses)
  • they are relatively inexpensive
  • B-lactams are organic acids and most soluble in water
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16
Q

Penicillin Binding Proteins

A
  • a set of transpeptidases that catalyze the final cross-linking reactions of peptidoglycan synthesis
  • found in quantities of several hundred to several thousand molecules per bacterial cell
  • two types of PBPs, low molecular weight PBPs and high molecular weight PBPs
  • the high MW PBPs- involved in different activities during peptidoglycan synthesis whereas the low PBPs function as D-alanine carboxypeptidases
  • inactivation of low MW PBPs is not thought to affect the viability of the cell
17
Q

How Do B-lactam’s work

A

-binds to the active site of the transpeptidase enzyme that cross-links the peptidoglycan strands by mimicking the D-alanyl-D-alanine residues that would normally bind to this site

18
Q

Carbapenem B-Lactams

A
  • B lactams with a broad spectrum of action
  • effective on gram positives, except MRSA
  • broad activity against gram negatives
  • slightly different structure than the other B-lactams, make them much more resistant to B-lactamase hydrolysis such as ESBL producers
  • wide diffusion in the body, especially in the CSF
19
Q

Glycopeptides and Lipoglycopeptides

A
  • glycopeptide: vancomycin- act by binding to D-alanyl-D-alanine residues thus preventing the cross linking of the peptitoglycan sheets
  • lipoglycopeptides- not FDA approved
20
Q

Inhibitors of Protein Synthesis

A

-tetracyclines
-aminoglycosides, macrolides, lincosamides,
phenicols
-ansamycins
-oxazolidinones

21
Q

Tetracyclines

A
  • Bacteriostatic- broad spectrum
  • primarily for treatment for Chlamydiae, Rickettsiae, and Mycoplasma
  • not recommended for pregnant women and children because of toxicity on bones and teeth of the fetus
  • glyclycyclines- new class, developed to overcome some of the more common tetracycline resistance mechanism
  • short acting (tetracycline)
  • intermediate (demeclocycline)
  • long acting (doxycycline)
22
Q

Aminoglycosides

A
  • Bind to the RNA of the 30S ribosomal subunit that affects all stages of normal protein synthesis- bacteriocidal activity- gentamycin, tobramycin
  • renal and ototoxicity- need to monitor blood levels
23
Q

Macrolides, Lincosamides, Streptogramins, Ketolides

A
  • bacteriostatic- their spectrum of activity is limited to gram positive cocci such as streptococci and staphylococci
  • these antibiotics are also active against anaerobes
24
Q

Phenicols: Chloramphenicol

A
  • very active against many gram-positive and gram-negative bacteria, chlamydia, mycoplasma, and Rickettsiae
  • resticted use of extra-intestinal severe salmonella infection
  • high toxicity, causes bone marrow aplasia and other hematological abnormalities
25
Q

Oxazolidinones: Linezolid

A
  • relatively new
  • gram positive infections
  • disrupts bacterial growth by inhibiting the initiation process in protein synthesis
  • because the site of inhibition is unique to linezolid cross- resistance to other protein synthesis inhibitors has not yet been reported
  • gram-negative bacteria appear to be naturally resistant
26
Q

Rifampin

A
  • bacteriostatic or bactericidal- depending on organism and concentration
  • primarily gram positive organisms and some gram negatives
  • used in combinations with other drugs to treat TB
  • used to treat carriers of N. meningitidis
  • used in combination with other antibiotics for severe Staphylcoccal infections including MRSA
27
Q

Inhibitors of membrane function

A
  • Lipopeptides- Polymyxins and Colistin

- Cyclic Lipopeptides- Daptomycin- FDA approval for skin/skin structure infections

28
Q

Antimetabolites: Folate Pathway Inhibitors

A
  • folic acid is essential for the synthesis of adenine and thymine
  • humans do not synthesize folic acid. Good selective target
  • sulfonamides- bacteriostatic, treat UTIs
  • trimethoprim-bactericidal (bactrim), broad spectrum, synergistic action
29
Q

Sulfonamides

A
  • pharmacokinetics- good urine solubility, high levels in urine
  • clinical uses- UTI, patients allergic to penicillins, otitis media
  • allergies may lead to Stevens- Johnson syndrome
  • Kernicterus, Hemolytic anemia
30
Q

Timethoprim/ Sulfamthoxazole Action

A
  • the drug resembles a microbial substrate and competes with the substrate for the limited microbial enzyme
  • the drug ties up the enzyme and blocks a step in metabolism
31
Q

Inhibitors of Nucleic Acid Synthesis

A
  • Quinolones
  • Fluoroquinolones
  • act by targeting topoisomerases which is responsible for cutting one of the chromosomal DNA strands at the beginning of the supercoiling process
32
Q

Furanes: Nitrofurantoin

A
  • inhibitor of nucleic acid synthesis
  • broad spectrum, bactericidal, oral
  • UTI caused by gram-negative and gram-positive organisms
  • the drug works by damaging bacterial DNA. In the bacterial cell, nitrofurantoin is reduced by flavoproteins
  • these reduced products are highly active and attack ribosomal proteins, DNA, respiration, pyruvate metabolism and other macromolecules within the cell

Microbiology/Immunology (46 decks)

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